Pre-processing assembly for pre-processing fuel feedstocks for use in a fuel cell system

ABSTRACT

A pre-processing assembly and method for processing fuel feedstock containing oxygen and hydrocarbons having higher and lower hydrocarbon content for a fuel cell, wherein the pre-processing assembly has a deoxidizing bed for reducing oxygen in the fuel feedstock and a pre-reforming bed for reducing higher hydrocarbon content in the fuel feedstock and wherein the deoxidizing bed and the pre-reforming bed are disposed within a common reaction vessel such that the fuel feedstock first passes through the deoxidizing bed and thereafter through the pre-reforming bed. The pre-reforming assembly may further include a propane processor bed for processing propane and propylene in the fuel feedstock, where the propane processor bed is disposed within the common reaction vessel with the deoxidizing bed and the pre-reforming bed.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of application Ser. No. 10/979,698,filed Nov. 2, 2004, the entire disclosure of which is herebyincorporated by reference.

BACKGROUND OF THE INVENTION

This invention relates to processing of fuel feedstocks containinghydrocarbons for use in fuel cell systems and, in particular, topre-processing assemblies for performing pre-processing of the fuelfeedstocks.

A fuel cell is a device which directly converts chemical energy storedin hydrocarbon fuel into electrical energy by means of anelectrochemical reaction. Generally, a fuel cell comprises an anode anda cathode separated by an electrolyte, which serves to conductelectrically charged ions. Molten carbonate fuel cells operate bypassing a reactant fuel gas through the anode, while oxidizing gas ispassed through the cathode. In order to produce a useful power level, anumber of individual fuel cells are stacked in series with anelectrically conductive separator plate between each cell.

Current fuel cells require as the reactant fuel gas a clean gas composedof hydrogen or a mixture of hydrogen and carbon monoxide. The reactantfuel gas is generally developed from a hydrocarbon-containing feedstockusing a reforming process. The hydrocarbon-containing feedstock usuallycontains substantial amounts of lower hydrocarbons, i.e., hydrocarbonswith 2 or less carbons, such as methane, as well as small amounts ofhydrogen, carbon dioxide, nitrogen and higher hydrocarbons, i.e.hydrocarbons with more than 2 carbons. This is true, for example, whenthe fuel feedstock is natural gas, peak shaving gas, digester gas andcoal bed methane.

The fuel feedstock is usually subjected to pre-processing to reduce oreliminate the higher hydrocarbons and to convert a portion of the lowerhydrocarbons to methane, hydrogen and carbon dioxide. The feedstock isthen further processed in a reforming unit to generate a fuel gas richin hydrogen.

Conventional pre-processing is carried out using a deoxidizer assemblyfollowed by a pre-reforming assembly. The deoxidizer assembly reducesthe concentration of oxygen in the fuel feedstock before the feedstockenters the pre-reforming assembly. This protects the catalyst (usually,a Ni-based catalyst) used in the pre-reforming assembly, which otherwisewould be deactivated in the presence of oxygen.

In the pre-reforming assembly, the reforming reaction is a conversionprocess which may inadvertently result in carbon formation based on fuelcomposition and steam. Carbon formation is of a particular concern whenthe fuel feedstock contains propylene, since the propensity to formcarbon increases as the concentration of propylene increases. The carbonwhich is produced deposits at the active sites of the reforming catalystof the pre-reforming assembly, thereby deactivating the catalyst. Thisreduces the life of the pre-reforming assembly.

In order to reduce carbon formation in conventional pre-reformingassemblies, special catalysts either containing alkali or based on anactive magnesia support have been proposed. Another technique is to useadiabatic processing. In such case, a fixed bed adiabatic pre-reformingassembly converts the higher hydrocarbon content at low temperature withsteam into methane, hydrogen and carbon oxides.

Propylene-containing fuel feedstocks generally have a high concentrationof sulfur-containing compounds. These compounds also tend to deactivatethe reforming catalysts in the pre-reforming assembly. Although fuelfeedstocks are typically desulfurized in a desulfurizer unit beforebeing carried to the pre-reforming assembly, high sulfur concentrationand the propylene in the fuel feedstocks reduce the capacity of thedesulfurizer unit.

Fuel feedstocks supplied to the pre-reforming assembly must also besupplied with additional hydrogen from a hydrogen supply. This isrequired to provide a sufficient concentration of hydrogen in thefeedstocks to maintain a reducing environment for the reformingcatalyst, thereby maintaining the catalyst activity.

As can be appreciated, conventional pre-processing of fuel feedstocks iscomplex and costly, due to the need for additional units or specialcomponents for supplying hydrogen, for reducing carbon formation and forremoving propylene and an additional unit to remove oxygen entering intothe pre-reforming assembly. A pre-processing assembly of simpler design,less cost and longer life would thus be desirable.

It is therefore an object of the present invention to provide apre-processing assembly which is better able to process fuel feedstockscontaining hydrocarbons and oxygen without deactivation of thepre-processing catalyst.

It is a further object of the invention to provide a pre-processingassembly which is capable of operating without an additional hydrogensupply and has an increased operating life.

It is yet a further object of the invention to provide a pre-processingassembly which is specifically adapted to retard the affects ofpropylene and other olefins in hydrocarbon containing fuel feedstocks.

SUMMARY OF THE INVENTION

In accordance with the principles of the present invention, the aboveand other objectives are realized in a pre-processing assembly andmethod for pre-processing a fuel feedstock containing hydrocarbonsincluding higher hydrocarbon content in which a common vessel housesboth a deoxidizing unit for reducing the oxygen content in the fuelfeedstock and a pre-reforming unit for receiving the fuel feedstockafter passage through the deoxidizing unit and for reducing the higherhydrocarbon content in the fuel feedstock. In performing thispre-processing the assembly also reduces a portion of the lowerhydrocarbon content in the feedstock and increases the hydrogen content.

In the embodiment of the invention disclosed herein, the pre-reformingunit is arranged to follow the deoxidizing unit along the flow path ofthe fuel feedstock and both units are in bed form. Also, in thisembodiment, the catalyst of the deoxidizing bed is one of a Pt—Pd onalumina catalyst or a Pt—Rh-based catalyst or a Rh—Pt-based aluminacatalyst and the catalyst of the pre-reforming bed is nickel-based andone of C11-PR (Sud Chemie), CRG-F (Johnson Matthey), CRG-LH (JohnsonMatthey) and G-180 (BASF).

In a further aspect of the invention, the pre-processing assemblyfurther includes a propane processor unit for processing propane andpropylene in the fuel feedstock. In the embodiment disclosed, thepropane processor unit is in bed form and arranged between thedeoxidizing bed and the pre-reforming bed. The propane processor bed hasa nickel-based carbon resistant catalyst, such as FCR-HC59 (Sud Chemie).

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and aspects of the present invention willbecome more apparent upon reading the following detailed description inconjunction with the accompanying drawings, in which:

FIG. 1 shows a fuel cell system having a fuel delivery system which usesa pre-processing assembly in accordance with the principles of thepresent invention;

FIG. 2 shows a detailed schematic view of a first embodiment of thepre-processing assembly of FIG. 1;

FIG. 3 shows a table of performance data of a deoxidizer of FIG. 2;

FIG. 4 shows a detailed schematic view of a second embodiment of thepre-processing assembly of FIG. 1;

FIG. 5 shows a graph of performance data of the pre-processing assemblyof FIG. 4;

FIG. 6 shows a graph of residual concentration of propane inpre-processed fuel feedstock leaving the assembly of FIG. 4 at differentfuel inlet temperatures;

FIG. 7 shows a bar graph of component concentrations in exitingpre-processed fuel feedstocks at different gas space velocities of inletHD-5 propane fuel feedstock gas;

FIG. 8 shows a bar graph of component concentrations in exitingpre-processed fuel feedstock at different gas space velocities of inletHD-5 propane fuel feedstock gas with five percent propylene;

FIG. 9 shows a table summarizing conditions during performance test andperformance results of the assembly of FIG. 4;

FIG. 10 shows a bar graph of component concentrations in exitingpre-processed fuel feedstock at different steam to carbon ratios ofinlet HD-5 propane fuel feedstock with five percent propylene;

FIG. 11 shows a graph of the effect of adding hydrogen to the fuelfeedstock gas input to the assembly of FIG. 4 on the exitingpre-processed fuel feedstock gas component concentrations.

DETAILED DESCRIPTION

FIG. 1 shows a fuel cell system 100 comprising a fuel delivery system101 having a pre-processing assembly 108 in accordance with theprinciples of the present invention. The fuel delivery system 101delivers hydrogen rich fuel to a fuel cell assembly 112 and includes afuel supply 102. The fuel supply 102 provides a fuel feedstockcontaining substantial amounts of methane and carbon oxides (CO andCO₂), and a higher hydrocarbon content, such as, for example, ethane,propane and C₄+ hydrocarbons, and amounts of oxygen and hydrogen.Typically, the fuel feedstock might be natural gas, peak shaving gas,digester gas, propane, coal bed methane, HD-5 or LPG.

The fuel delivery system 101 also includes a desulfurizer 104, apreheater 106 and a reformer 110. The fuel feedstock from the fuelsupply 102 is passed to the desulfurizer 104, where sulfur-containingcompounds in the fuel feedstock are physically and/or chemicallyremoved. Desulfurized fuel feedstock then flows to the pre-heater 106where it is preheated to a suitable temperature, e.g., approximately375° C., before being carried to the fuel pre-processing assembly 108.Pre-processed fuel feedstock exiting the assembly 108 is suitable foruse in a fuel cell assembly 112. In the fuel cell assembly 112, thehydrogen-rich fuel undergoes an electrochemical reaction to producepower.

As discussed in detail herein below, in accordance with the principlesof the present invention, the pre-processing assembly 108 includes aplurality of fuel processing units disposed or housed in a common vesselfor deoxidizing the fuel feedstock and for pre-reforming the deoxidizedfuel feedstock to reduce or substantially eliminate the higherhydrocarbon content. This pre-reforming processing also reduces thelower hydrocarbon content by converting it to hydrogen so that theresultant pre-processed fuel feedstock exiting the assembly 108 hasincreased hydrogen content and methane suitable for high temperaturefuel cell applications.

A detailed schematic view of a first embodiment of the pre-processingassembly 108 is shown in FIG. 2. As shown, the pre-processing assembly108 includes two fuel processing units in the form of a deoxidizer bed204 and a pre-reforming bed 206. These beds are arranged or housed in acommon vessel 202 having an inlet 208 for receiving the preheated fuelfeedstock from the preheater 106 and an outlet 210 for discharging thepre-processed fuel feedstock to the fuel cell assembly 112.

As shown, the pre-reforming bed 206 is arranged to follow the deoxidizerbed 204 along the flow path 201 of the feedstock. Also, a porous member,shown as a screen 212 which typically can be made of Nickel mesh havinga mesh size of 10-14, separates the beds and provides support for thebed 204. The pre-processing bed 206, in turn, is supported on the lowersurface 202 a of the vessel 202.

The deoxidizer bed 204 comprises a deoxidizing catalyst which typicallymight be Pt/Pd on Alumina, or G-74D, manufactured by Sud Chemie Inc.Other catalysts such as Pt—Rh based catalysts and Rh—Pd based Aluminacatalysts also may be used.

The catalyst used in the pre-reforming bed 206 may be a standard nickelbased catalyst. Examples are nickel-based alumina catalysts, or C11-PRcatalyst, manufactured by Sud-Chemie Inc. Additionally, othernickel-based catalysts such as CRG-F and CRG-LH, manufactured by JohnsonMatthey or G-180 manufactured by BASF may likewise be used.

The shapes of the catalysts used in both beds may vary. For example, inthe case shown, pellet-shaped catalysts are employed in both thedeoxidizer bed 204 and the pre-reforming bed 206. In addition,monolith-based catalyst structures, comprising a ceramic monolithsubstrate with a catalyst coating, are suitable for use in each bed.

As mentioned above, the pre-processing assembly 108 reduces orsubstantially eliminates the higher hydrocarbon content and the oxygencontent in the fuel feedstock. It also reduces the lower hydrocarboncontent and increases the hydrogen content in the feedstock. Due to thearrangement of the deoxidizer and pre-reforming beds 204 and 206 in thecommon vessel 202, the pre-processing reduces the possibility ofdeactivating the catalysts in the beds and is carried out without theneed of adding hydrogen from a hydrogen supply to the fuel feedstock.

In particular, the catalyst of the deoxidizer bed 204 facilitates theremoval of oxygen from the fuel feedstock. Where the feedstock is coalmine methane or digester gas, the oxygen is removed by reacting theoxygen with the methane in the feedstock aided by the catalyst, asfollows:

2CH₄+O₂→2CO+4H₂+heat

CH₄+O₂→CO₂+2H₂+heat

Where the feedstock is peakshaving gas, the oxygen is removed in thedeoxidizer bed 204 by reacting the propane in the feedstock with oxygen,as follows:

C₃H₈+2O₂→2CO+2CO₂+4H₂+heat

Removal of oxygen in the deoxidizer bed 204 prevents the deactivation ofthe catalyst in the pre-reforming bed 206. It also produces additionalhydrogen needed to maintain a reducing environment for such catalyst. Inthe pre-reforming bed 206, the reduction of the higher hydrocarboncontent in the deoxidized feedstock is aided by the catalyst and occursby conversion of the higher hydrocarbon content into a mixture ofhydrogen, carbon oxides and methane. A reduction in the lowerhydrocarbon content also occurs through conversion and results inincreased hydrogen and carbon oxides. Particularly, approximately 10% ofthe methane in the fuel is reformed to provide hydrogen for theelectrochemical reaction in the fuel cell assembly. The remainder of themethane in the fuel is internally reformed in the fuel cell assembly.The following reactions exemplify the conversion processing:

CnHm+nH₂O→nCO+(m/2+n)H₂

CH₄+H₂O→CO+3H₂

C₃H₈+2H₂O→CO₂+2CH₄+2H₂

As mentioned above, the deoxidizer bed 204 is firstly disposed in thevessel 202 in relation to the direction of the flow or flow path 201 ofthe fuel feedstock and to the inlet of the vessel 202. The pre-reformingbed 206 then follows the deoxidizer bed 204 in the direction of the flowpath 201. As was stated previously, this arrangement causes the removalof oxygen from the fuel feedstock before entering the pre-reforming bed,thereby preventing deactivation of the catalyst in the bed. The life ofthe pre-processing assembly 108 is thus extended.

As can also be seen from the above, the deoxidizing and pre-reformingreactions in the beds 204 and 206 increase the hydrogen content in thefeedstock. This maintains a reducing environment in the pre-reformingbed 206. In particular, back diffusion of hydrogen in the pre-reformingbed 206 provides this reducing environment, thereby allowing theassembly 108 to operate without an additional supply of hydrogen to thefuel feedstock.

The amount of back diffusion of hydrogen in the bed 206 is inverselyrelated to the space velocity of the fuel feedstock. Accordingly,maintaining a low space velocity of the fuel feedstock through thepre-reforming bed 206 is desired in order to realize sufficient hydrogenback diffusion in the bed.

As can be appreciated, the space velocity is directly proportional tothe flow of the fuel through the pre-reforming bed 206 and inverselyproportional to the volume of the catalyst in the pre-reforming bed 206.Accordingly, the space velocity of the fuel feedstock can be controlledby adjusting the volume of the catalyst in the pre-reforming bed 206and/or by changing the amount of the fuel flowing through the reformingbed 206, using the following relationship:

${SV} = \frac{{Fuel}\mspace{14mu} {Flow}\mspace{14mu} {per}\mspace{14mu} {hour}}{{Catalyst}\mspace{14mu} {Volume}}$

In addition to controlling the space velocity of the fuel feedstock, thesuperficial velocity of the fuel needs to be controlled for a desiredamount of hydrogen back diffusion. Superficial velocity is a function ofa diameter of the vessel through which the fuel is flowing.Particularly, superficial velocity is directly proportional to the fuelflow and inversely proportional to the diameter of the pre-reforming bed206.

In the pre-processing assembly 108 of the present invention, spacevelocities between 2,000 to 5,000 h⁻¹ and maximum superficial velocitiesof approximately 1.3 ft/s have been found desirable in operation of thepre-reforming bed 206.

Moreover, the pre-reforming bed 206 may additionally be adapted to actas a guard to trap sulfur-containing compounds present in the fuelfeedstock which are not removed by the desulfurizer unit 104 of FIG. 1.In particular, the nickel in pre-reforming catalyst is suitable fortrapping sulfur-containing compounds effectively. With this additionalsulfur removal, the operating life of the reforming catalyst in the fuelcell assembly 112 can be increased.

The optimal design of the pre-reforming assembly 108 will depend uponthe particular application. Some of the important factors to beconsidered are the requirements of the fuel cell assembly 112, the typeof fuel gas being processed, and the amount of gas to be treated. Anillustrative example of a pre-reforming assembly 108 is described hereinbelow.

EXAMPLE 1

The pre-processing assembly 108 has been optimized for processing fuelfeedstock comprising oxygen and methane for use in a 300 kW Direct FuelCell power plant. The deoxidizer bed 204 comprises a G-74D catalyst andhas a volume of 0.7 cubic feet. The pre-reforming bed 206 comprises aC11-PR catalyst and has a volume of 2.5 cubic feet. The deoxidizer bed204 is approximately 4 inches in thickness and the pre-reforming bed 206is approximately 14.5 inches in thickness. The common vessel 202 is madefrom 304/310 stainless steel and has a volume of 4 cubic feet and adiameter of 20 inches.

The optimal temperatures of the fuel feedstock entering the vessel 202through the inlet 208 and of the pre-processed fuel feedstock exitingthe vessel 202 through the outlet 210 are approximately 300 to 490° C.The optimal operating temperature range of the deoxidizer bed 204 isbetween 300° C. and 600° C., and the optimal operating temperature rangeof the pre-reforming bed 206 is between 320° C. and 540° C. The spacevelocity of the fuel feedstock flowing through the deoxidizer bed 204 isbetween 5,000 and 12,000 h⁻¹ and the space velocity of the fuelfeedstock flowing through the pre-reforming bed 206 is between 2,000 and5,000 h⁻¹. Moreover, in order to maintain a desired hydrogen backdiffusion in the pre-reforming bed 206, the desired maximum superficialvelocity of the fuel feedstock flowing through the bed 206 is 1.3 ft/sat STP conditions.

The performance of the pre-processing assembly 108 was tested by passingthrough the assembly 108 fuel feedstock comprising 6.31 lb-mole/hr ofmethane, 0.06 lb-mole/hr of carbon dioxide, 12.48 lb-mole/hr water, 0.08lb-mole/hr of nitrogen, 0.17 lb-mole/hr of ethane and 0.03 lb-mole/hr ofpropane. The temperature of the fuel feedstock entering the deoxidizerbed 204 was approximately 425° C. and the space velocity of the fuelfeedstock was approximately 10,000 hr⁻¹. The temperature of thepre-processed fuel leaving the pre-reforming bed 206 was about 320° C.,and the space velocity of the pre-reformed fuel leaving thepre-reforming bed 206 was about 3,000 hr⁻¹. Fuel pre-processed using thepre-processing assembly comprised about 1.67 lb-mole/hr of hydrogen,6.25 lb-mole/hr of methane, 0.53 lb-mole/hr of carbon dioxide, 11.54lb-mole/hr of water and 0.08 lb-mole/hr of nitrogen. From theseperformance results, it can be seen that all of the ethane or propanepresent in the fuel feedstock was converted to methane, hydrogen andcarbon dioxide in the assembly 108.

Example 2

In this example, the pre-processing assembly 108 of Example 1 has alsobeen optimized for processing hydrocarbon fuels contaminated with up to10% oxygen. The optimal temperature range of the fuel feedstock enteringthe vessel 202 through inlet 208 is approximately 310° C. to 500° C.

The deoxidizing function of the pre-processing assembly 108 of FIG. 2has been demonstrated with fuels containing oxygen such as anaerobicdigester gas, coal mine methane, and peak shave gas. The deoxidizingperformance of the assembly 108 of this example was tested at variedinlet temperatures of the fuel feedstock entering the assembly 108, andvaried oxygen contents of the hydrocarbon fuels. FIG. 3 shows tabulateddata of deoxidizer performance summarizing the results of these tests.In the testing procedure, the oxygen content of the inlet fuel feedstockwas measured, and the fuel feedstock was pre-heated to varioustemperatures ranging from 312° C. to 439° C. before entering theassembly 108. The concentration of oxygen in the pre-processed fuelfeedstock gas exiting the deoxidizer bed 204 and the temperature, atdeoxidizer and pre-reformer bed interface were measured. The flow rateof the fuel feedstock through the assembly was 15 standard cubic feetper minute (scfm) of natural gas, with the diluents, such as carbondioxide, nitrogen, propane and air, added as listed in FIG. 3, or, forpeak shave gas, at a predetermined ratio so as to give the same heatingvalue. The fuel feedstock used during these tests had a steam to carbonratio of 2.0.

As the tabulated data of FIG. 3 show, pre-processed fuel feedstockleaving the assembly 108 was depleted of all oxygen. The temperaturerise across the deoxidizer bed 204 is an indication of the reaction ofoxygen with the hydrocarbon fuel feedstock. Accordingly, these testsshow that the deoxidizer bed 204 is capable of removing oxygen from fuelfeedstock over a wide temperature range and over a wide variation inconcentration of contaminant oxygen in the inlet fuel feedstock.

A pre-processing assembly 108 having this construction is estimated tohave a life of approximately 5 years as compared to an average 3-yearoperating life of a conventional assembly. The life of thepre-processing assembly 108 is increased partly due to the maintenanceof the pre-reforming bed 206 in a reducing atmosphere by providinghydrogen from the deoxidizer and from optimized hydrogen back diffusion,thereby increasing the overall life of the pre-reforming catalyst.

In accordance with a further aspect of the invention and to furtherimprove the performance and the operating life of the pre-processingassembly 108 when the fuel feedstock includes propane and/or propylene,the assembly 108 is additionally adapted as shown in FIG. 4. Moreparticularly, FIG. 4 shows a second embodiment of the pre-processingassembly 108 of FIG. 2 modified to include a propane processor bed 301,adapted to convert propane and propylene in the fuel feedstock tomethane and carbon oxides.

As shown in FIG. 4, the propane processor bed 301 is disposed in thevessel 202 between the deoxidizer bed 204 and the pre-reforming bed 206.In particular, the bed 301 is situated below the screen 212 and rests ona further like screen 302 which separates the bed 301 from the bed 206.The fuel feedstock thus now flows through the deoxidizer bed 204 inwhich oxygen reduction occurs, through the bed 301 in which propane andpropylene are removed through conversion to methane and carbon oxidesand through the bed 206 in which pre-reforming causes a reduction in thehigher hydrocarbon content and conversion of a part of the lowerhydrocarbon content to hydrogen.

In the embodiment of FIG. 4, the beds 204 and 206 contain the samecatalysts as those discussed above for the first embodiment of FIG. 2.The propane processor bed 301, in turn, comprises a nickel-based carbonresistant catalyst doped with promoters such as cerium oxide, lanthanumoxide, palladium, platinum, or a combination of these compounds. Anexample of a suitable nickel-based carbon resistant catalyst is FCR-HC59manufactured by Sud Chemie. The carbon resistant catalyst in the propaneprocessor bed 305 is selective towards propane and propylene andpromotes the conversion of propane and propylene in the fuel feedstockto methane and carbon oxides, as follows:

C₃H₆+2H₂O→CO₂+2CH₄+H₂

C₃H₈+2H₂O→CO₂+2CH₄+2H₂

The pre-processing assembly 108 of FIG. 4 is able to process commercialgrade propane fuel comprising up to 5% propylene, or HD-5 gas. Theperformance of the pre-processing assembly will vary depending on thefuel feedstock inlet temperature, the space velocity of the fuelfeedstock in the beds 204, 301, 206, and the steam to carbon (“S/C”)ratio of the fuel feedstock.

As with the embodiment of FIG. 2, the optimal design of thepre-reforming assembly 108 of FIG. 4 will vary depending on the factorsdiscussed for the embodiment of FIG. 2 and the additional factor of thepropylene concentration. An illustrative example of a configuration ofthe pre-processing assembly 108 of FIG. 4 is described in Example 3below.

Example 3

The pre-processing assembly of FIG. 4 has been optimized for processingfuel comprising propane and up to 5% propylene for use in a 300 kWDirect Fuel Cell power plant. The deoxidizer bed 204 comprises a G-74Dcatalyst and has a volume of 0.7 cubic feet. The propane processor bed301 comprises an FCR-HC59 anti-carbon catalyst manufactured by SudChemie and has a volume of 0.75 cubic feet, and the pre-reforming bed206 comprises a C11-PR catalyst and has a volume of 1.7 cubic feet. Thevessel 202 is made from 304/310 stainless steel and has a volume of 4cubic feet.

The optimal temperature of the fuel feedstock entering the vessel 202through the inlet 208 is approximately 350° C. and the temperature ofthe pre-processed fuel exiting the vessel 202 through the outlet 210 isapproximately 350° C. The deoxidizer bed 204 is adapted to operate at atemperature between 300° and 600° C., while the propane processor bed301 and the pre-reforming bed 206 are adapted to operate at temperaturebetween 300° and 540° C. The optimal operating temperature range of beds204, 301 and 206 of the assembly 108 is between 300° C. and 400° C. Thedesired space velocity of the fuel feedstock flowing through thedeoxidizer bed 204 is between 5,000 and 12,000 h⁻¹. The desired spacevelocity of the fuel feedstock flowing through the propane processor bed301 is between 5,000 and 11,000 h⁻¹, while the desired space velocity ofthe fuel feedstock flowing through the pre-processing bed 206 is between2,000 and 5,000 h⁻¹. Moreover, it is preferred that the steam to carbonratio of the fuel feedstock entering the assembly is approximately 3.

The performance of the pre-processing assembly 108 of FIG. 4 was testedusing propane fuel feedstock having various concentrations of propylene.Fuel feedstock used during these tests comprised pure propane with nopropylene, HD-5 gas having 2538 ppm of propylene, and HD-5+ gas havingapproximately 5% propylene. The tests were performed at varied inlettemperatures of the fuel feedstock entering the assembly 108, variedspace velocities and varied steam to carbon ratios.

FIG. 5 shows a graph of performance data resulting from the testing ofthe assembly 108 of FIG. 4 at different fuel feedstock inlettemperatures. In the testing procedure, fuel feedstock was pre-heated tovarious temperatures before entering the assembly 108 and theconcentrations of the various components of the pre-processed fuelfeedstock gas exiting the assembly were measured. The fuel feedstockused during this testing had a steam to carbon ratio of 3.0. The flowrate of the pure propane fuel feedstock gas through the assembly was at5.0 standard cubic feet per minute (“scfm”), the flow rates of the HD-5fuel feedstock gas and the HD-5+ fuel feedstock gas were at 4.5 scfm andthe inlet temperatures of the fuel feedstock gas entering the assembly108 ranged between 300 and 450° C.

As shown in FIG. 5, pre-processed fuel feedstock leaving the assembly108 included methane, hydrogen and carbon dioxide content. The X-axis inFIG. 5 represents the pre-processing assembly inlet temperature, whilethe Y-axis represents the exit concentration of each of the componentsexiting in the pre-processed fuel feedstock gas.

As can be seen from FIG. 5, the respective concentrations of methane,hydrogen and carbon dioxide in the exiting pre-processed fuel feedstockgas resulting from the pure propane input feedstock are approximatelythe same as the respective concentrations of methane, hydrogen andcarbon dioxide in the exiting pre-processed fuel feedstock gas resultingfrom the HD-5 and HD-5+ input feedstocks. Accordingly, these tests showthat the assembly 108 is capable of pre-processing fuel feedstock withhigh propylene concentrations without degradation in performance.

As can also be seen, as the inlet temperature of the feedstockincreased, the concentration of hydrogen in the exiting pre-processedfuel feedstock gas also increased, while the concentration of methane inthe exiting pre-processed fuel feedstock gas decreased. Moreover, asshown, at all inlet temperatures the pre-processed fuel feedstock gasexiting the assembly included a sufficient concentration of hydrogen tomaintain the pre-reforming catalyst in a reducing atmosphere, thusextending the operating life of the assembly 108.

FIG. 6 shows a graph of residual propane concentration in the exitingpre-processed fuel feedstock gas of the assembly 108 of FIG. 4corresponding to various inlet temperatures of the feedstock. As shownin FIG. 6, the X-axis represents the inlet temperature of the feedstockentering the pre-processing assembly 108, and the Y-axis represents apercent concentration of propane in the exiting pre-processed fuelfeedstock gas. As can be appreciated, the performance of the assembly isinversely related to the residual propane concentration in the exitingpre-processed fuel feedstock gas.

FIG. 6 shows that in all cases, even with lower inlet temperatures ofapproximately 300° C., the concentration of propane in the exitingpre-processed fuel is acceptably low. Furthermore, the concentration ofpropane in the exiting pre-processed fuel feedstock gas decreases as theinlet temperature of the fuel feedstock increases, to a point wherepropane is non-detectable at inlet temperatures above 425° C.

Based on the above tests performed at different fuel feedstock inlettemperatures, it can be seen that the performance of the assembly 108 isexcellent over a wide temperature range, allowing the inlet temperatureto be varied according to the desired outlet concentrations of hydrogenand methane. The optimal operating temperatures for the pre-processingassembly of FIG. 4 are between 300 and 450° Celsius.

The effect of fuel feedstock space velocity on the performance of thepre-processing assembly 108 of FIG. 4 was also tested using HD-5 andHD-5+ input fuel feedstock gases. During these tests, fuel feedstockswere passed through the assembly 108 with the gas space velocities of1900 h⁻¹, 2660 h⁻¹, 3420 h⁻¹, and 9082 h⁻¹. The inlet temperature of thefuel feedstock was kept constant at 375° C. Percent concentrations ofmethane, hydrogen and carbon dioxide in the pre-processed fuel feedstockgas exiting the assembly 108 were recorded.

FIGS. 7 and 8 show bar graphs of exit gas concentrations, with constantinlet temperature of 375° C., at different feedstock space velocities ofHD-5 and HD-5+ fuel feedstocks, respectively, flowing through theassembly 108. The Y-axis in FIGS. 7 and 8 represents the percentconcentration of each component in the exiting pre-processed fuelfeedstock gas. As can be seen, the assembly 108 is able to effectivelypre-process fuel feedstock flowing through it with a space velocity inthe range of 1900 h⁻¹ and 9082 h⁻¹ and demonstrates excess capacity inthis space velocity range. Additionally, these tests show that theperformance of the assembly 108 is not greatly affected by an increasein the concentration of propylene in the HD-5+ fuel feedstock when itsspace velocity is in the range of 1900 h⁻¹ to 9044 h⁻¹.

The performance of the assembly 108 of FIG. 4 has also been tested atother inlet temperatures with high space velocity for both HD-5 propanewith added propylene and natural gas. FIG. 9 shows a table summarizingspecific conditions during these tests, including fuel feedstockcomposition and inlet temperatures, and exit compositions ofpre-processed natural gas and HD-5 propane with added propylene gasexiting the assembly 108 of FIG. 4. In particular, the inlet feedstockcomposition of natural gas includes 2.23% of ethane, 0.36% of propaneand 0.16% of butanes, while the inlet feedstock composition of HD-5propane with added propylene includes 7.2% of ethane, 88% of propane,4.02% of propylene and 0.6% of butanes. As shown in FIG. 9, all of thesehigher hydrocarbons were removed by the pre-processing assembly 108. Asthese tests show, the assembly 108 of FIG. 4 has excellent performanceat space velocities in the range of 12,000 h⁻¹ for the deoxidizer 204,11,000 h⁻¹ for the propane processor 301, and 5,000 h⁻¹ for thepre-reformer 206.

Furthermore, the performance of the assembly 108 of FIG. 4 was tested atdifferent steam to carbon ratios. FIG. 10 shows a bar graph of thecomponent concentrations in the exiting pre-processed fuel feedstock gasderived from HD-5+ fuel feedstock at different steam to carbon ratios.The tests were conducted with a constant fuel feedstock inlettemperature of 375° C. In FIG. 10, the Y-axis represents the percentconcentration of the exit gas components. Performance testing wascarried out by passing a mixture of HD-5+ fuel feedstock and steam withsteam to carbon ratios of 2.9, 3.0, 3.2 and 3.4 through the assembly108. Concentrations of methane, hydrogen and carbon dioxide in theexiting pre-processed fuel feedstock gas were measured at the outlet ofthe assembly 108. As can be seen, an increase in the steam to carbonratio from 3.0 to 3.4 resulted in an increased hydrogen production bythe assembly.

The performance of the assembly 108 was also tested with propane fuelfeedstock to which was added different hydrogen concentrations. Fuelfeedstock used during this test comprised 5 scfm of propane and 39 scfmof steam (steam to carbon ratio of 2.6) and had an inlet temperature of310° C. Different amounts of hydrogen were added to the fuel feedstockat the inlet of the assembly 108. FIG. 11 shows a graph of the effect ofhydrogen added to the fuel feedstock on the concentrations of methane,propane, hydrogen and carbon dioxide in the exiting pre-processed fuelfeedstock gas. As shown, the concentration of propane increased as theamount of hydrogen added at the inlet of the assembly 108 increased.These tests show that the assembly 108 is capable of operating withoutan additional hydrogen supply, and that the addition of hydrogenresulted in decreased conversion of propane, thus detracting from theperformance of the assembly.

In all cases it is understood that the above-described arrangements aremerely illustrative of the many possible specific embodiments whichrepresent applications of the present invention. Numerous and variedother arrangements can be readily devised in accordance with theprinciples of the present invention without departing from the spiritand the scope of the invention. For example, various modifications ofthe catalyst bed construction of the invention may be made to optimizethe space velocity and the superficial velocity of the fuel feedstockgas as it is being passed through the pre-reforming bed. Moreover, otherdeoxidizing and pre-reforming catalysts may be used in the beds 202 and204 in lieu of those discussed above.

1. A fuel processing method for processing fuel feedstock for a fuelcell, the fuel feedstock including oxygen and hydrocarbons having higherand lower hydrocarbon content, the fuel processing method comprising thesteps of: providing said fuel feedstock; reducing oxygen in said fuelfeedstock using a deoxidizing unit having a deoxidizing bed; reducingsaid higher hydrocarbon content in said fuel feedstock using apre-reforming unit having a pre-reforming bed; wherein said deoxidizingunit and said pre-reforming unit are disposed within a common vesselsuch that said fuel feedstock first flows through said deoxidizing unitand thereafter through said pre-reforming unit, and wherein: thepre-reforming bed of said pre-reforming unit is sized such that thespace velocity of said fuel feedstock in said pre-reforming unit isbetween 2,000 and 5,000 h⁻¹ and the superficial velocity of said fuelfeedstock in said pre-reforming unit is such as to provide a desiredamount of hydrogen back diffusion; and the deoxidizing bed of saidoxidizing unit is sized such that the space velocity of said fuelfeedstock in said deoxidizing unit is between 5,000 and 12,000 h⁻¹.
 2. Afuel processing method according to claim 1, wherein said deoxidizingbed of said deoxidizing unit and said pre-reforming bed of saidpre-reforming unit are such that said pre-reforming bed follows saiddeoxidizing bed along the flow path of said fuel feedstock.
 3. A fuelprocessing method according to claim 2, wherein said deoxidizing bedcomprises a deoxidizing catalyst and said pre-reforming bed comprises apre-reforming catalyst.
 4. A fuel processing method according to claim3, wherein said deoxidizing catalyst is one of Pt—Pd on aluminacatalyst, Pt—Rh-based catalyst and Rh—Pd-based alumina catalyst, andwherein said pre-reforming catalyst is a nickel-based catalyst.
 5. Afuel processing method according to claim 4, wherein said deoxidizingcatalyst is G-74D.
 6. A fuel processing method according to claim 4,wherein said pre-reforming catalyst is one of C11-PR, CRG-F, CRG-LH andG-180.
 7. A fuel processing method according to claim 2, furthercomprising a step of reducing the propylene in said fuel feedstock usinga propane processor unit.
 8. A fuel processing method according to claim7, wherein said propane processor unit is disposed in said common vesseland comprises a propane processing bed.
 9. A fuel processing methodaccording to claim 8, wherein said deoxidizer bed, said pre-reformingbed and said propane processing bed are disposed in said common vesselsuch that said fuel feedstock flows first through said deoxidizing bed,and then through one of said propane processing bed and saidpre-reforming bed, and thereafter through the other of said propaneprocessing bed and said pre-reforming bed.
 10. A fuel processing methodaccording to claim 9, wherein said propane processing bed comprises anickel-based carbon resistant catalyst.
 11. A fuel processing methodaccording to claim 10, wherein said carbon resistant catalyst isFCR-HC59.
 12. A fuel processing method according to claim 1, whereinreducing said oxygen in said deoxidizing bed produces hydrogen, and saidlower hydrocarbon content is converted to produce hydrogen in saidpre-reforming bed.
 13. A fuel processing method according to claim 12,wherein the maximum superficial velocity of said fuel feedstock in saidpre-reforming unit is approximately 1.3 ft/s at STP conditions.
 14. Afuel processing method according to claim 1, further comprising removingsulfur-containing compounds from said fuel feedstock in saidpre-reforming unit.